Cryptic exception when key not found

[hrj]

When a key is not found while evaluating an expression, it throws an exception.

It should be converted to an error.

For example, the following will throw an exception in current release:

def xyz = someUndefinedKey

[hrj]

It is working as expected in the definition line. Now need to fix the reference error within a post's expression. For example:

2016/may/1
  account             someUndefinedRef